Multilayer ceramic structures are used in a variety of fields, particularly for microelectronic components, for example, in telecommunications, for producing large-scale integrated pressure sensors or other sensors, for example, in the field of high-frequency technology, or for producing microfluid components.
One important and cost-effective method for producing multilayer ceramic structures of this type is “Low Temperature Cofired Ceramics”, which will be abbreviated in what follows to “LTCC”. In this technique, the required structures, such as conductor tracks, depressions, capacitors, resistors, coils, feedthroughs, etc., are inserted into or applied to unfired ceramic films (e.g., green films). These green films are then individually structured and then stacked and laminated. The laminated green film composite is then sintered.
For various applications, for example, for fluid or sensor applications, channel structures or other hollow cavities, adapted accordingly in terms of size, are required in a multilayer ceramic structure of this type.
To produce miniaturized channel structures, according to conventional methods, channel structures are introduced into green films of this type by means of, for example, stamping, laser, or embossing techniques, and must be stabilized in subsequent processing steps using pastes or films that contain graphite, or using organic materials, such as polymethylmethacrylate (“PMMA”). The stabilizing material escapes during the sintering process. With the known methods for producing channel structures, structures that are larger than 100 μm (laterally) and a maximum of 20 μm (vertically) can typically be produced. However, many applications require channel structures that have considerably smaller lateral and vertical dimensions to allow optimum adjustment of the dielectric constants. Moreover, it is disadvantageous that with the known processes, the volatility of the stabilizing material must be adjusted to the liquid phase sintering process and/or to the solidification of the glass phase, in order to ensure a complete escape of the stabilizing material.
A problem addressed by the present invention is therefore that of providing a simple and cost-effective method for producing a ceramic multilayer structure, with which hollow cavities and therefore channels or membrane structures can be produced, which have minimum dimensions of a few μm (horizontally and/or vertically) and typical maximum dimensions of a few 100 μm (horizontally), or have a tape layer (vertically), and which do not have the above-described problems relating to the stabilizing material. A problem is further that of providing a corresponding multilayer structure.
The present invention is directed toward overcoming one or more of the above-identified problems.